the muzzle is bored to accept a short sleeve that is soldered in, then reamed to the choke you want.i don't know if thin wall choke tubes might be a better idea unless you don't like choke tubes.i think Brownells sells the sleeve so you could look them up to get an idea of what they are. mc
FWIW my money would be on thin-walled choke tubes like Briley makes. You would have much more flexibility and the modification most likely will leave the gun no less "original" than sleeving. Briley thin walls tend to pattern nicely, too.
